Switched mode power supplies (SMPS) are widely used in various types of automotive, industrial, household or consumer electronic applications. A switched mode power supply includes at least one electronic switch coupled to at least one inductor of an inductive rectifier circuit. A switched mode power supply is configured to receive an input power which is given by an input current multiplied with an input voltage at an input and supply an output power which is given by an output voltage multiplied with an output current to a load coupled to an output. By regulating the input power received at the input the switched mode power supply may regulate at least one operation parameter, for example, the output voltage, the output current, or the input current. The input power is regulated by regulating a current through the at least one inductor, whereas the inductor current is regulated by a switched mode operation of the at least one electronic switch.
The switched mode operation of the at least one electronic switch may include operating the electronic switch in a plurality of successive drive cycles, with each drive cycle including an on-time in which the at least one electronic switch is switched on and an off-time in which the at least one electronic switch is switched off. Furthermore, the switched mode operation may include switching on the at least one electronic switch at a predefined switching frequency and varying a duration of the on-time.
The switched mode operation of the at least one electronic switch may cause interferences. If the switching frequency is a fixed frequency an energy of a frequency spectrum of the interferences (interference spectrum) is concentrated at the fixed frequency and its harmonics. By modulating the switching frequency around a center frequency the energy of the interference spectrum can be distributed over a certain frequency range. In each case, however, it is undesirable for the interferences to reach a power source such as a power grid connected to the input. This is defined by standards such as CISPR Class A and Class B or IEC/EN 61000-3-2. In order to meet these standards an attenuation of the interferences by a filter coupled between the input and the at least one electronic switch may become necessary. Such a filter may account for a considerable share of the size and cost of the power supply.
It is therefore desirable to have a switched mode power supply that provides for an efficient filtering of interferences at low cost and low size.